Multi function tempreature sensor

[Dr. Ian McArthur]

Marc, I have been following your posts re the MFTS.  There are two different
versions of these.  One is electronically operated (with a four-terminal
connection) and one is mechanical (with a three-terminal connector).  I have
just been diagnosing a similar problem with my 1988 5000TQ which I am quite
certain is related to the warm-up systems in the CIS.  I think there are
three factors affecting the mixture as the engine warms up.

 

First is the cold start valve which squirts extra fuel into the intake
manifold for a few seconds when the engine is cold.  This works regardless
of a low fuel pressure which will prevent the injectors from opening.

 

Second is the warm-up pressure regulator on the side of the engine block
which enriches the mixture to compensate for a cold engine over the warm up
period.

 

Third is the MFTS which apparently does much more than prevent over-boost in
a hot engine.  I think it also controls mixture values electronically
depending on coolant temperature.  Maybe the "ordinary" coolant temperature
sensor also affects this.

 

I am lucky enough to have two identical 88 5000TQs and buckets of parts.  I
am in the process of changing these out sequentially while monitoring the
control pressure with a gauge I have fitted with a tee into the control
pressure fuel line. 

 

Unfortunately I have had to stop for a few days because we are in the midst
of our first winter snow and I will not work on the car inside my shop when
I am messing with fuel.

 

I have a considerable volume of articles and notes which I would be happy to
share.  From these notes I think I have a really good idea of how the CIS in
the 88TQs works.